accelerate internal error

mats.hs

import qualified Data.Array.Accelerate as A
import qualified Data.Array.Accelerate.CUDA as A

-- (v1 `outer` v2) . (v1 - v2)
h :: A.Vector Double -> A.Vector Double -> A.Vector Double
h v1 v2 = A.run $ accOuter v1' v2' `accApply` A.zipWith (-) v1' v2'
    where !v1' = A.use v1
    	  !v2' = A.use v2

-- outer product
accOuter :: A.Acc (A.Vector Double) -> A.Acc (A.Vector Double)
         -> A.Acc (A.Array A.DIM2 Double)
accOuter xs ys = A.zipWith (*) xsRepl ysRepl
  where
    n           = A.size xs
    m           = A.size ys

    xsRepl      = A.replicate (A.lift (A.Z A.:. A.All A.:. m  )) xs
    ysRepl      = A.replicate (A.lift (A.Z A.:. n   A.:. A.All)) ys

-- matrix vector mult
accApply :: A.Acc (A.Array A.DIM2 Double) -> A.Acc (A.Vector Double) -> A.Acc (A.Vector Double)
accApply m v = let A.Z A.:. rows A.:. _ = A.unlift (A.shape m) :: A.Z A.:. A.Exp Int A.:. A.Exp Int
               in A.generate (A.index1 rows)
                             (\ix -> A.the (v `accDot` takeRow (A.unindex1 ix) m))

-- get a whole row from a matrix
takeRow :: A.Exp Int -> A.Acc (A.Array A.DIM2 Double) -> A.Acc (A.Vector Double)
takeRow n mat =
  let A.Z A.:. _ A.:. cols = A.unlift (A.shape mat) :: A.Z A.:. A.Exp Int A.:. A.Exp Int
  in A.backpermute (A.index1 cols)
                   (\ix -> A.index2 n (A.unindex1 ix))
                   mat

-- dot product for vectors
accDot :: A.Acc (A.Array A.DIM1 Double) -> A.Acc (A.Array A.DIM1 Double) -> A.Acc (A.Scalar Double)
accDot xs ys = A.sum (A.zipWith (*) xs ys)

-- then, criterion calls h:
-- ...
-- bgroup "accelerate" [ bench "100" $ whnf (h a1) a2 ]
-- ...
-- where 
--        !a1 = (A.Z A.:. 100) `A.fromList` [1..100]
--        !a2 = (A.Z A.:. 100) `A.fromList` [0..99]

-- the error
{-
benchmarking accelerate/100
mats: 
*** Internal error in package accelerate ***
*** Please submit a bug report at https://github.com/AccelerateHS/accelerate/issues
./Data/Array/Accelerate/Trafo/Sharing.hs:447 (convertSharingExp): inconsistent valuation @ shared 'Exp' tree with stable name 72;
  env' = [74]
-}